Erik K. Insko

Sodium NMR evaluation of articular cartilage degradation

One of the first effects of degenerative osteoarthritis is the loss of proteoglycans from the matrix of articular cartilage. Using a model of osteoarthritic change where the cartilage has been enzymatically degraded with trypsin, the sodium NMR characteristics of the cartilage were determined as a function of changes in the proteoglycan content. The results demonstrate that the single quantum sodium signal decreases as the proteoglycan content of the cartilage matrix decreases. In addition, the relaxation characteristics of the sodium change such that the T1 is longer, the T2s is longer, and the T2f is shorter. Short echo‐time, T1‐weighted sodium images are presented which demonstrate that this information may be utilized to detect the loss of proteoglycans from articular cartilage. Magn Reson Med 41:30‐34, 1999.

Volumetric measurement of human calf muscle from magnetic resonance imaging

Muscle mass is a determining factor in skeletal muscle function and is affected by inactivity, immobilization, disease, and aging. The aim of this study was to develop an objective and timeefficient method to quantify the volume and cross-sectional area of human calf muscles using three-dimensional magnetic resonance images. We have estimated the errors incurred in muscle volume measurements arising from artifacts known to occur in magnetic resonance imaging (MRI). The largest source of error was due to partial volume effects, which resulted in overestimation of phantom volumes ranging from 145 to 900 cc by 6% to 13%. The magnitude of this effect has been shown to increase with decreasing object size and decreasing spatial resolution. We have presented a straightforward correction for this effect, which has reduced the volume measurement error to less than 4% for all cases. Through the use of computer simulations, the correction algorithm has been shown to be independent of object shape and orientation. To reduce user subjectivity, a semiautomated computer program has been developed to segment MRI data for particular muscle groups. Images from seven human subjects were analyzed by the program, yielding muscle volumes of 154.2±23.2, 281.2±35.8, and 432.2±83.7 for the lateral gastrocnemius, medial gastrocnemius, and soleus, respectively.

In vivo sodium MR imaging of the intervertebral disk at 4 T

RATIONALE AND OBJECTIVES The authors performed this study to evaluate whether a semiquantitative method of in vivo sodium imaging of the human intervertebral disk could provide diagnostic quality images in a reasonable time. MATERIALS AND METHODS In vivo sodium imaging of the human spine was performed with a 4-T whole-body magnetic resonance (MR) unit by using custom-built hardware and software. Short-echo-time images were obtained with a modified three-dimensional gradient-echo sequence, a custom-built surface coil, and receiver modifications to allow for nonproton data acquisition. Corrections for surface coil image intensity were performed with phantom image data. An estimation of the fixed charge density within the intervertebral disk was made with the surface coil-corrected images by using cerebrospinal fluid as an internal reference standard. RESULTS In vivo sodium images of the spine with high signal-to-noise ratio and resolution were obtained in approximately 10 minutes. Correction of in vivo images for surface coil effects demonstrated that the sodium content of the cerebrospinal fluid in the spinal canal may be used as an internal standard to estimate the proteoglycan content of the intervertebral disk. CONCLUSION Diagnostic quality in vivo sodium images of the intervertebral disk are technically feasible and may be useful for assessing the proteoglycan content of the intervertebral disk. This would provide a method to detect early degenerative changes in the disk and evaluate the effects of any subsequent therapy.

17O-decoupled 1H detection using a double-tuned coil.

17O-decoupled proton MR spectroscopy imaging with a double-tuned radiofrequency (RF) coil at 2 T was used to detect and quantify H2 17O in tissue containing various concentrations of 17O-enriched water in 5% gelatin. The pulse sequence used in these experiments consisted of a conventional proton spin-echo sequence with RF irradiation at the 17O resonance frequency applied between the proton 90 degrees pulse and the signal acquisition window. The double-tuned coil provided several advantages over systems using separate RF coils for 17O decoupling and proton excitation/detection, including ensuring that the same (or similar) sample volumes are excited and decoupled and permitting accurate calibration of the 17O decoupling pulse amplitude. The efficiency of 17O decoupling as a function of decoupling RF amplitude, decoupling duration, and decoupling resonance offset was investigated. Finally, the specific absorption rate of the 17O decoupled pulse sequence was investigated and found to lie within federal guidelines at 1.5 T.

Indirect detection of lung perfusion using susceptibility-based hyperpolarized gas imaging†

To address the problem of inadequate signal‐to‐noise ratio (SNR) encountered in lung perfusion magnetic resonance imaging (MRI) by developing an indirect detection based on the strong hyperpolarized (HP) gas signal.

Subacute clot mimicking flow in a thrombosed arterial bypass graft on two-dimensional time-of-flight and three-dimensional contrast-enhanced MRA.

Subacute intravascular thrombus can contain methemoglobin, which results in very short spin‐lattice (T1) relaxation times. We describe a case of a 78‐year‐old man with increasing right lower extremity claudication. The patient had a thrombosed arterial bypass graft showing high signal intensity that mimicked flow on both two‐dimensional time‐of‐flight and three‐dimensional contrast‐enhanced MR angiography. Misinterpretation of the high signal thrombus as flowing blood can be avoided by obtaining a precontrast T1‐weighted sequence. J. Magn. Reson. Imaging 2000;11:192–194.